1. Technical Field
The technical field relates to an ink jet head and an ink jet device having the same.
2. Background Art
An ink jet head is known as a head that can apply a required amount of ink toward an object in a certain timing in accordance with an input signal. Particularly, since a piezoelectric (piezo) ink jet head can apply many kinds of ink with accurate control, it has been actively developed to date. In general, the piezoelectric ink jet head includes an ink supply path, a plurality of ink chambers communicating with the ink supply path and having a nozzle, and a piezoelectric element that applies pressure to ink filled in the ink chambers. By applying a driving voltage to the piezoelectric element, mechanical deformation occurs on the piezoelectric element, and pressure is applied to the ink inside the ink path to cause the ink to discharge from the nozzle.
For example, as a representative construction of the ink jet head, a construction in which the entire surface of an actuator (piezoelectric element) is installed on a resin film (side wall of an ink chamber) is known, and there is a technique of discharging ink drops from the nozzle by pressing the ink filled in the path through pressing of the resin film by the driving of the piezoelectric element (see FIG. 4 and Paragraph [0079] of JP-A-2006-096042).
Also, as an invention that aims at high density of ink drops, an ink jet recording head as described in JP-A-3-015555 (FIGS. 3 and 4) is known. The ink jet recording head is related to a technique of discharging ink from an ink nozzle by changing the volume of an ink pressure chamber that is formed of a cavity plate through displacement of an SiO2 film portion by pressing an Si projection portion using a piezoelectric actuator (see FIG. 10 of JP-A-3-015555). Also, FIG. 2 of JP-A-2005-262638, FIGS. 1 and 2 of JP-A-11-058731, FIGS. 1 and 2 of JP-A-4-355147, FIG. 1 of JP-A-6-064163, FIGS. 2 and 3 of JP-A-6-297700, Paragraph [0015] of JP-A-6-143573, FIG. 1 of JP-A-8-224874, and FIG. 1 of JP-A-2001-010050 disclose techniques to the effect that a relay member, which is provided between a piezoelectric element and a vibrating plate, extends in one direction, and is arranged to be in contact with a portion of the piezoelectric element. In addition, ink jet heads disclosed in JP-A-2008-254196, JP-A-2000-233502, JP-A-11-077996, US Patent Application Publication No. 2008/0238980, U.S. Pat. No. 6,286,938, U.S. Pat. No. 7,128,406, JP-A-07-178899, JP-A-02-141243, JP-A-10-114081, U.S. Pat. No. 5,956,058, and U.S. Pat. No. 6,609,785 are known.
However, the above-described ink jet heads in the related art have the following problems.
First, the technique described in FIG. 4 and Paragraph [0079] of JP-A-2006-096042 represents a construction in which the actuator (pressing means) is arranged on the entire surface of the pressing plate (vibration plate) that forms the upper surface of the pressure chamber. Because of this, in the construction as in JP-A-2006-096042 (FIG. 4, Paragraph 0079), when ink is discharged from the nozzle, the pressure that is applied from the actuator to the pressure chamber is transferred to not only the nozzle but also other places of the pressure chamber, and thus it may not be possible to concentrate the pressure from the corresponding actuator onto the nozzle portion. Accordingly, in the technology described in JP-A-2006-096042 (FIG. 4, Paragraph 0079), sufficient discharge force may not be provided when the ink is discharged from the nozzle. Also, in JP-A-2006-096042 (FIG. 4, Paragraph 0079), a construction in which the width of the actuator (for example, the width of the actuator 58 in FIG. 4 of JP-A-2006-096042 (FIG. 4, Paragraph 0079)) is narrowed and the actuator is arranged only just above the nozzle 51 may be considered. However, in the construction in which the actuator is simply small-sized, the pressure that is applied to the ink chamber is reduced to that extent, and thus the discharge force of the ink is lowered.
Also, in JP-A-2006-096042 (FIG. 4, Paragraph 0079), it may be considered to narrow the width of the actuator and to heighten the driving voltage that is applied to the actuator. However, if the driving voltage is heightened, the actuator itself has heat, and the temperature of the ink that flows through the ink chamber is heightened to cause a non-preferable result. Also, the heightening of the driving voltage is related to the lifespan of the actuator itself. Also, in the construction in which the width of the actuator is narrowed and the actuator is arranged only just above the nozzle, a desired discharge force is secured by stacking the actuator, but the ink jet head becomes large-sized due to the large actuator to cause a non-preferable result.
Next, FIGS. 3 and 4 of JP-A-3-015555 discloses the construction in which the piezoelectric actuator is connected to the vibrating plate 7 through the Si projection portion 10. Since the technique described in FIG. 3 of this document aims at high density of the ink jet nozzle, the Si projection portion is arranged only in the position that corresponds to the ink nozzle. Accordingly, as shown in FIG. 6B of this document, when the pressure is applied to the ink pressure chamber by the piezoelectric actuator, the pressure is applied in every direction, and thus a portion of the ink flows backward to the ink supply side. This may be a great obstacle to the discharge of the ink from the ink nozzle.
In the techniques described in FIG. 2 of JP-A-2005-262638, FIGS. 1 and 2 of JP-A-11-058731, FIGS. 1 and 2 of JP-A-4-355147, FIG. 1 of JP-A-6-064163, FIGS. 2 and 3 of JP-A-6-297700, Paragraph [0015] of JP-A-6-143573, FIG. 1 of JP-A-8-224874, and FIG. 1 of JP-A-2001-010050, there is no approach to the circulation of ink in the ink jet head. In the structure in which the relay member, which is provided between the piezoelectric element and the vibrating plate, extends in one direction, and is arranged to be in contact with a portion of the piezoelectric element as in FIG. 2 of JP-A-2005-262638, FIGS. 1 and 2 of JP-A-11-058731, FIGS. 1 and 2 of JP-A-4-355147, FIG. 1 of JP-A-6-064163, FIGS. 2 and 3 of JP-A-6-297700, Paragraph [0015] of JP-A-6-143573, FIG. 1 of JP-A-8-224874, and FIG. 1 of JP-A-2001-010050, the ink is simply discharged from the nozzle, and thus, for example, the ink may stay in a corner portion of the ink chamber or may become stiff. Accordingly, the corresponding structure is not sufficient as the ink jet head.